The present invention relates to N,N'-bis-(trans-4-isocyanatocyclohexyl)urea obtained by the reaction in an inert solvent of a cyclohexane-1,4-diisocyanate ("CHDI") having a high transisomer content and water. The urea according to the invention, which may contain a small portion of oligomeric ureas, may advantageously be used for the synthesis of polyurethanes.
It is known that monoisocyanates react with water to form N-substituted carbamic acid derivatives which can be converted into urea derivatives, with concomitant liberation of carbon dioxide, by a reaction with further quantities of isocyanate. Polyureas are obtained analogously from diisocyanates and water by polyaddition.
It is also known that under certain reaction conditions, low molecular weight urea diisocyanates of the following general formula ##STR1## may be isolated from the reaction mixture obtained when 1 mol of water reacts with at least 2 mol of a diisocyanate at low temperatures (that is, about 0.degree. to 30.degree. C.) in a solvent. According to DAS No. 1,101,394, only those diisocyanates in which the two isocyanate groups differ in their reactivity, for example, 2,4-tolylenediisocyanate, are suitable for this reaction. Aliphatic diisocyanates are less suitable because of their low reactivity with water. Thus, although urea diisocyanates have already been described generally, no diisocyanato urea based on CHDI has been described specifically.
When attempts are made to react commercial CHDI with water in an inert solvent under the usual conditions previously known in the art, only small quantities of polymeric urea with low NCO content are obtained, even when basic catalysts and long reaction times are employed. This observation is also in agreement with the formation of urea described by S. W. Wong and K. C. Frisch in Adv. in Urethane Sci. and Technol, 8, 75-92 (1981), their account of a kinetic investigation. According to Wong and Frisch, the reaction of highly dilute solutions of trans-CHDI with water in cellosolve acetate at 50.degree. C. resulted in a polyurea with a half life of 3623 minutes and an isocyanate content approaching 0%.
It has now surprisingly been found that N,N'-bis(4-isocyanatocyclohexyl)urea (optionally containing only a small proportion of oligomeric ureas) may be obtained in a high yield when cyclohexane-1,4-diisocyanate having a high transisomer content reacts with water in a molar ratio of 2:1 at low temperatures (about 40.degree. C.) in inert solvents at a concentration of 10% by weight (based on the solvent used) in the presence of basic catalysts.
The urea according to the invention can advantageously by used for the synthesis of polyurethane elastomers which have excellent mechanical properties as well as outstanding thermal stability. Moreover, the unpleasant properties of the starting diisocyanates, namely the pungent odor and lachrymatory effect due to the low vapor pressure, do not occur in the corresponding urea, so that it can advantageously be processed more simply and safely.